In opthalmology a known and frequently employed surgical procedure is to replace an eye's natural lens by an artificial (synthetic) one (“intraocular lens”). During this surgical intervention the natural lens is removed from its lens-capsule bag (explantation), after which an intraocular lens is inserted (implantation) into the remaining lens-capsule bag (capsula lentis). The explantation of the natural lens in practice involves destruction and extraction of the lens tissue (phacolysis), in general by phacoemulsification, during which the lens is emulsified (liquefied) by shock waves generated by means of an ultrasonic probe or a laser (photolysis) and is then removed by suction. The synthetic intraocular lens can be a prefabricated, rigid body mounted in the capsule bag by way of a supporting means (haptic device), but can also be a soft, yielding body or even be injected into the capsule bag as a free-flowing mass. When a flexible or yielding intraocular lens is used, it can accommodate—i.e., adjust its optical focal length—just as the natural lens does, by way of the ciliary muscles and the zonular fibres as well as the lens-capsule bag. The use of folding lenses or injectable lenses enables the surgical incision to be reduced, in practice to only 3 mm or even less. For the intraocular lens it is customary to use polymer materials that are transparent in the visible spectrum, in particular polymethyl methacrylate (PMMA) or silicone (polysiloxane elastomer) or acrylic.
Replacement of the natural eye lenses by a synthetic intraocular lens is at present employed only to eliminate a cataract, i.e. a cloudy lens. However, other cases for application are also possible, although more rarely encountered in practice: for example, an intraocular lens can be employed to adjust or correct the optical focal length, e.g. in cases of short-sightedness (myopia) or far-sightedness (hyperopia), or after accidents or injuries to the lens in which the lens-capsule bag itself is not irreparably damaged.
The document U.S. Pat. No. 5,324,282 A discloses a surgical instrument in the form of a needle for destroying tissue, which is designed to remove cataracts in optical surgery, i.e. to remove the lens of the eye by photolysis. This known instrument comprises a tubular outer wall with a longitudinal axis and a free end, as well as an optical fibre from a laser and an aspiration channel, each of which is longitudinally oriented and passes through the interior of the needle as far as its free end. At the free end of the needle a target made of titanium (Ti) is disposed, separated by some distance from the free end of the laser fibre, the fibre and the target being adjusted with respect to one another so that the laser beam from this fibre strikes the target. At the free end of the needle is also provided a tissue-aspiration port, disposed at an angle and laterally offset, into which the aspiration channel opens and which is disposed immediately adjacent to the target and the space between the end of the laser fibre and the target. By way of a suction pump a vacuum is created in the aspiration channel, by means of which the tissue to be destroyed is sucked up to the aspiration port and fractured, after which the individual fragments of the tissue are sucked away through the aspiration channel. When the tissue is in contact with or has been sucked against the tissue-aspiration port by the low pressure, laser pulses are shot out of the laser fibre and onto the target, the energy in these pulses being sufficient to produce an optical breakdown at the target material and hence generate a shock wave that strikes the tissue at the tissue-aspiration port and tears it into small pieces, which are then sucked away through the aspiration channel. The laser light is preferably generated with a neodymium-YAG laser and has a wavelength of 1,064 nm. The laser pulses have a pulse duration of 8 ns and a pulse repetition rate of 20 pulses per second. Hence the laser energy is 100 mJ per second and the energy of each pulse, 5 mJ. Furthermore, there can also be provided within the needle a longitudinally oriented irrigating tube to conduct flushing fluid through an outlet disposed at the side.
The document U.S. Pat. No. 5,906,611 A discloses a further development of the instrument known from U.S. Pat. No. 5,324,282 A, in which the target has a stepped structure, such that each step has two surfaces, one of which is oriented perpendicular to the needle axis and the other parallel thereto; the sequence of steps rises from an outer side, at the outside wall of the needle, towards the tissue-aspiration port. As a result, in each step zone of the target, as the target material evaporates the shock wave thus produced is not blocked by another part of the target in the direction towards the aspiration port. With a neodymium-YAG laser pulses can be produced with repetition rates between 2 and 50 pulses per second and pulse energies between 2 and 15 mJ. The pulse duration can be set between 8 and 12 ns. Preferably the pulse repetition rate is set at between 2 and 6 pulses per second and the pulse energy, between 6 and 10 mJ. For a cataract operation between 200 and 800 pulses or shots are used.
A laser handpiece constructed like those in U.S. Pat. No. 5,324,282 A and U.S. Pat. No. 5,906,611 A, together with a digital control and supply device that comprises a laser for the laser pulses as well as a venturi pump for aspirating the tissue parts, has for years been successfully marketed by the firm of A.R.C. Laser GmbH and was successfully employed in a large number of operations. Here aspiration occurs by way of the laser handpiece and irrigation with an electrolytic flushing solution (BSS) is done by way of a second instrument, in a bimanual technique. The product is sold under the name “Lyla/Pharo”. For the actual eye operation employing this known device, various surgical techniques are used.
One problem with surgical explantation or phacolysis of the natural eye lens and the subsequent implantation of an artificial intraocular lens is the subsequent growth and proliferation of the epithelial cells that constitute the epithelium covering the inner surface of the lens-capsule bag. During this postoperative complication the newly formed epithelial cells migrate around the inserted artificial lens or even into it, eventually obscuring vision through the lens. This phenomenon is referred to as posterior capsule opacification (PCO), and when it follows a cataract operation it is also called a secondary cataract.
To alleviate this problem of postoperative proliferation of the epithelial cells in the capsule bag, various solutions have been suggested and employed. These can be subdivided as follows:    1. The removal of epithelial cells from the inner surface of the capsule bag during or after explantation of the eye lens and before implantation of the intraocular lens;    2. Preventing growth of the epithelial cells of the lens-capsule bag after implantation of the intraocular lens; and    3. Producing a hole or tear in the capsule bag by means of a laser, as a result of which the tissue of cells forming the epithelium is likewise torn apart (photodisruption, capsulotomy).
The removal of the epithelial cells is undertaken either by taking them away with a surgical instrument, such as a needle, or else chemically by applying substances toxic to cells or biochemically by antibodies.
So that after implantation of an intraocular lens the growth of remaining epithelial cells of the lens-capsule bag over the intraocular lens can be prevented or at least minimized, various measures are known, for example the use of special intraocular lenses, the surfaces of which are provided with structures such as pits or projections over which the epithelial cells cannot very easily grow, or are coated with growth-inhibiting cytotoxic substances; alternatively, growth-inhibiting cytotoxic substances can be implanted in the capsule bag itself, or an implant with photoactivatable immobilising substances can be inserted, as proposed in DE 199 55 836 C1. In the case of the opthalmological implant according to DE 199 55 836 C1 the pharmaceutical cytotoxic agent is released by photoactivation at a later time following the operation, at the earliest after the wound has completely healed, so as to kill off the epithelial cells on the lens and prevent the growth of new epithelial cells there. The chemical or biochemical removal of lens epithelial cells and prevention of their proliferation is described in EP 0 372 071 B1. The chemical removal of lens epithelial cells is furthermore described in Patent Abstracts of Japan 04352719 A.
A good survey of the known methods and devices for removing epithelial cells from the lens-capsule bag or of methods and substances to prevent growth of the epithelial cells can be found in the printed documents DE 199 55 836 C1 and EP 0 372 071 B1.
A fundamental problem associated with the known methods and apparatus for removing the epithelial cells by means of or during a surgical intervention resides in the fact that in no case have the epithelial cells been completely removed, in particular because certain places, e.g. along the equator and immediately behind the iris, are not readily accessible to the surgeon and because the chemical agents that are used ought not to be too aggressive on account of the danger of also damaging the capsule bag and adjacent eye regions, as well as the problem that wound healing may be impaired. However, if epithelial cells remain in the lens capsule, the risk of proliferation is always present.